Rigid articles, particularly containers, made of thermoplastic materials have been used to package a wide variety of consumer goods products, such as in the cosmetic, shampoo, laundry, and food categories. For such articles, having a unique and desirable shape is important. One design element in rigid articles is the use of well-defined corners. These well-defined corners are used to define, for example, a shoulder portion of a bottle. In a specific example, the VIDAL SASSON® (The Procter & Gamble Company) shampoo bottle has well-defined corners (alternatively “sharp corners”) near the top of the bottle that contribute to the iconic look of the bottle. The so called “square shoulders” provide a unique point of equity (in the myriad of shampoo bottles available in the marketplace) that are recognized by consumers.
Many rigid articles, such as bottles, are made with resins: PE (Polyethylene), PP (Polypropylene) or PETG [Poly (ethylene terephthalateco-1,4-cylclohexylenedimethylene)], or the combination thereof. These resin(s) are co-extruded (along with additional multiple materials) into a parison at a temperature higher than the melting temperature of the resin. After the parison is formed, it is blown with pressure against a mold to form the desired three-dimensional shape of the article. The blow molded article demolds around ambient temperature. Often PETG is used in the outermost layer of the parison/blown article to deliver a high gloss effect. These aforementioned resins are generally able to produce well-defined corners because the associated extrusion blow molding (EBM) process requires the resin material to flow and to be blown at a temperature considerably higher than the resin's melting temperature. Consequently, the heated resins flow easily thereby penetrating the limited spaces of the mold that define the corresponding corner(s) of the rigid article.
However, there are at least one or more disadvantages in using the EBM platform (and the aforementioned resins). Since EBM requires multiple different resins to deliver high gloss effects to the article, the combination of materials may pose recycling challenges. Translucency or transparency is sometimes a desired appearance effect in the article. Generally, standard EBM process has challenges in providing this effect, especially when PE or PP resin is used. The use of multiple number of resins and/or other materials to provide any of these aforementioned effects increases complexity and cost from a processing as well as logistical perspectives.
There is a growing trend in the use of PET, or modified PET comprising materials, in an injection (stretch) blow molding (IBM or ISBM) process. Generally, PET in an I(S)BM platform has flexibility in delivering different appearance effects to articles. These effects include high transparency to high opacity; and mirror-like shininess to a matte finish. However, a problem with typical PET in the I(S)BM platform is the ability to form well-defined corner(s). Without wishing to be bound by theory, the problem with forming these well-defined corners is because the PET resin is typically blown at relative low temperature, e.g., generally between glass-transition temperature (“Tg temperature) and cold-crystallization peak temperature (“Tcc temperature”). Consequently, this resin is hard to deform and difficult to be blown into the corresponding corners of the mold.
Accordingly, there is a need to have one or more of the advantages associated with traditional PET materials and I(S)BM platform but also having the ability to form articles with well-defined corner(s) (that is otherwise generally available with PE/PP and EMB platform) as to deliver a fuller palette of design options to articles.